Using a Voltage Regulator to vary motor speed.

Thread Starter

BarryBozeman

Joined Apr 1, 2016
41
Hi Everyone-
This post is probably mainly about my misunderstanding about how a Voltage Regulator works, so please bear with me.

I am using an LM350, which I believe is similar to the LM317, save for a higher rating for amperage.

The goal is to drive a 6v DC Motor.

It seems that I am able to get a voltage from nearly 6v to around 1.25v - the latter, of course, is the voltage specified in the datasheet, as some kind of reference voltage established by a resistor across the "adjust pin" and the Vout pin.

Unfortunately, the DC motor keeps rolling along at 1.25v. I think I need to be able to range from 6v to 0v. Can anyone explain to me how I might get the full range of expression? Thanks.
 

BR-549

Joined Sep 22, 2013
4,938
I believe you have some things confused. But, we need to see your circuit. What voltage are you feeding the regulator with? Have you read the data-sheet? It explains the reference and suggest several circuits for you.
 

dendad

Joined Feb 20, 2016
3,517
Do you have a -ve supply to the output goes to 0V?

But a much better way to control a motor is Pulse Width Modulation (PWM).
Variable voltage supply is really not the way to go for so many reasons. Have a look at PWM on the internet.
 

Picbuster

Joined Dec 2, 2013
998
Do you have a -ve supply to the output goes to 0V?

But a much better way to control a motor is Pulse Width Modulation (PWM).
Variable voltage supply is really not the way to go for so many reasons. Have a look at PWM on the internet.
Controlling the power of a dc motor with voltage is not the way to do it. Current is generating power.( the motor is using coils to transfer energy to a rotating shaft).
Yes, I know no current without voltage.

Dendad is correct using PWM is the way to go.
PWM keeps the voltage constant while the duration as function of time will change.
PWM is extreme simple to build use a pic 12f675 plus a fet to control the motor.
Advantage you have complete control over rep rate( block interval), density (bits per block) and percentage power per bit. eq one byte on 256= full power but a value of 128 does not mean 50% power on the motor shaft)

Picbuster
 

dl324

Joined Mar 30, 2015
10,722
+1 for PWM. You can make your own using an opamp and a comparator. Use the opamp to make a triangle wave and a comparator to determine duty cycle for the motor.

This is one case where using an opamp as a comparator would be acceptable to keep parts count to a minimum. A dual opamp , a handful of passives, and a BJT/MOSFET.
 

crutschow

Joined Mar 14, 2008
24,938
Below is an example 555 PWM circuit.
Pot U2 controls the PWM duty-cycle and thus the motor speed.
The N-MOSFET, M1, must be a logic-level type (Vgs max threshold ≤2V).

How much current does the motor take?

upload_2018-10-12_8-59-20.png
 
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